Transition metals

• Transition metals


  Elements where the d sub-level in atoms or ions is incomplete
• Transition metal elements


  • Sc
  • Ti
  • V
  • Cr
  • Mn
  • Fe
  • Co
  • Ni
  • Cu
  • Zn
• Transition metal characteristics arise from an incomplete d sub-level in atoms or ions
• Electron configurations of transition metals

  • Sc: 1s22s22p63s23p6 4s23d1
  • Ti: 1s22s22p63s23p6 4s23d2
  • V: 1s22s22p63s23p6 4s23d3
  • Cr: 1s22s22p63s23p6 4s13d5
  • Mn: 1s22s22p63s23p6 4s23d5
  • Fe: 1s22s22p63s23p6 4s23d6
  • Co: 1s22s22p63s23p6 4s23d7
  • Ni: 1s22s22p63s23p6 4s23d8
  • Cu: 1s22s22p63s23p6 4s13d10
  • Zn: 1s22s22p63s23p6 4s23d10
• Electron configurations of transition metal ions

  • Sc 3+: [Ar] 4s03d0
  • Ti 3+: [Ar] 4s03d1
  • V 3+: [Ar] 4s03d2
  • Cr 3+: [Ar] 4s03d3
  • Mn 2+: [Ar] 4s03d5
  • Fe 3+: [Ar] 4s03d5
  • Co 2+: [Ar] 4s03d7
  • Ni 2+: [Ar] 4s03d8
  • Cu 2+: [Ar] 4s03d9
  • Zn 2+: [Ar] 4s03d10
• Transition metals lose 4s before 3d when forming ions
• Why is zinc not a transition metal?

  Zinc can only form a +2 ion. In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its compounds.
• Transition metal characteristics


  • Complex formation
  • Formation of coloured ions
  • Variable oxidation state
  • Catalytic activity
• Complex


  A central metal ion surrounded by ligands
• Ligand


  An atom, ion or molecule which can donate a lone electron pair
• Coordinate bonding


  The shared pair of electrons in the covalent bond come from only one of the bonding atoms
• Coordination number


  The number of coordinate bonds formed to a central metal ion
• Monodentate ligands


  • H2O, NH3 and Cl-
• Bidentate ligands


  • NH2CH2CH2NH2 and ethanedioate ion C2O4

  2-
• The transition elements are the d-block elements, which have partially filled or empty d orbitals.
• Multidentate ligands


  • EDTA4-
• Substitution reactions


  1. Ligands can be exchanged without change of coordination number

  2. Ligands can be exchanged with change of coordination number
• Addition of a high concentration of chloride ions to an aqueous ion


  Leads to a ligand substitution reaction with a change in coordination number
• Complexes formed with chloride ions


  • [CuCl4]2-
  • [CoCl4]2-
  • [FeCl4]-
• If solid copper chloride (or any other metal) is dissolved in water it forms the aqueous [Cu(H2O)6]2+ complex and not the chloride [CuCl4]2- complex
• Formation of bidentate complexes


  1. [Cu(H2O)6]2+ + 3NH2CH2CH2NH2 → [Cu(NH2CH2CH2NH2)3]2+ + 6H2O

  2. [Cu(H2O)6]2+ + 3C2O4

  1. → [Cu(C2O4)3]4- + 6H2O
• Formation of multidentate complexes


  [Cu(H2O)6]2+ + EDTA4- → [Cu(EDTA)]2- + 6H2O
• The substitution of monodentate ligand with a bidentate or a multidentate ligand leads to a more stable complex. This is called the chelate effect.
• Chelate effect


  Increase in entropy due to increase in moles of products, creating more disorder
• The stability of the EDTA complexes has many applications
• EDTA titrations


  [Cu(H2O)6]2+ + EDTA4- → [Cu(EDTA)]2- + 6H2O
• Shapes of complex ions

  • Octahedral
  • Tetrahedral
  • Square planar
  • Linear
• Types of stereoisomerism in complex ions

  • Cis-trans isomerism
  • Optical isomerism
• Cis-trans isomerism in square planar complexes

  • cis-[Ni(NH3)2Cl2]
  • trans-[Ni(NH3)2Cl2]
• Cis-trans isomerism in octahedral complexes


  • cis-[Cr(H2O)4Cl2]+
  • trans-[Cr(H2O)4Cl2]+
• Optical isomerism in octahedral complexes


  • [Co(NH2CH2CH2NH2)3]2+
• Colour changes


  Arise from changes in oxidation state, coordination number or ligand
• Colour arises from electronic transitions between d orbitals
• Changing a ligand or coordination number

  Alters the energy split between the d-orbitals, changing ΔE and hence the frequency of light absorbed
• d block element


  Transition metal
• Sc3+ ion has no d electrons left to move around, so there is not an energy transfer equal to that of visible light
• Zn2+ ions and Cu+ ions have a full d shell (3d10), so there is no space for electrons to transfer and therefore no energy transfer equal to that of visible light
• In the equation [Co(H2O)6]2+ + 6 NH3 [Co(NH3)6]2+ + 6H2O, both the ligand and the coordination number are changing
• In the equation O2, only the oxidation state is changing
• A solution will appear blue if it absorbs orange light. The energy split in the d orbitals ΔE will be equal to the frequency of orange light(5 x1014 s-1) x Planck's constant